Breaking the limit: Biological countermeasures for space radiation exposure to enable long-duration spaceflight.

Concerns over the health effects of space radiation exposure currently limit the duration of deep-space travel. Effective biological countermeasures could allow humanity to break this limit, facilitating human exploration and sustained presence on the Moon, Mars, or elsewhere in the Solar System. In this issue, we present a collection of 20 articles, each providing perspectives or data relevant to the implementation of a countermeasure discovery and development program. Topics include agency and drug developer perspectives, the prospects for repurposing of existing drugs or other agents, and the potential for adoption of new technologies, high-throughput screening, novel animal or microphysiological models, and alternative ground-based radiation sources. Long-term goals of a countermeasures program include reduction in the risk of radiation-exposure induced cancer death to an acceptable level and reduction in risks to the brain, cardiovascular system, and other organs.